β-Lactamase-producing Branhamella catarrhalis causingotitis media in children

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additional 24% are sensitive to the initial therapy, and the majority (57%) have bacteriologically negative middle-ear fluid. Clinical failure in the group without antimicrobial resistance is unexplained. The antimicrobial sensitivity of a given bacterial species is determined in vitro with a fixed inoculum of bacteria, usually in the range of 104 to 105 CFU/ml. If the inoculum exceeds 105 , the concentration of antibiotic required to inhibit the growth of the organism may increase considerably for common bacterial pathogens such as H. influenzae ~ and B. catarrhalis, 2 particularly if they are betalactamase producers. Colony counts in infected body fluids vary considerably. The cerebrospinal fluid in bacterial meningitis commonly has a concentration of bacteria that exceeds 106 and may even reach 108 CFU/ml; the density of bacteremias is usually < l03 CFU/ml. 4-6 In our study the concentration of bacteria in middle-ear fluid of patients with acute otitis media frequently exceeded 104 and occasionally 105 CFU/ ml. As expected, the Gram stain of middle ear fluid was positive in most instances when the colony count exceeded 104 CFU/ml. This observation is consistent with the fact that bacteria in a variety of body fluids (e.g., unspun urine, blood, and cerebrospinal fluid) are not usually easily detected unless they are present in concentrations approximately 105 CFU/ml? The absence of a more perfect correlation between the findings on Gram stain and colony count may be related to the quality of the middle-ear fluid. The volume delivered by a calibrated loop may be less reproducible when the fluid is thick and viscous. In patients with acute otitis media, clinical failures and persistent or recurrent effusions are poorly understood, particularly when tympanocentesis yields antibiotic-sensitive microorganisms. Noncompliance with orally administered antimicrobial regimens or inadequate duration of therapy may explain some instances of clinical failure. It could be speculated that initially high bacterial colony counts may be one of the factors determining outcome in the treatment of acute otitis media. We thank Helen Schorner for secretarial assistance.